1. Field of the Invention
The present invention relates to an apparatus for measuring particle-size distribution of a powder which is used or produced in a powder industry, such as cement- and ceramics-industry.
2. Description of the Prior Art
The prior art apparatuses of this kind include a sieving apparatus, an apparatus wherein the sedimentation of a powder in a suspension having been formed by dispersing the powder in a liquid is detected by measuring the solid content in liquid, the specific gravity, or the intensity of transmitted light, an apparatus in which a dispersed powder is irradiated by a beam of light and the intensity of scattered light is measured, and an apparatus wherein a lazer beam is passed through a dispersed powder and the particle-size distribution is determined from the obtained diffraction pattern.
However, each of the aforementioned various apparatuses has some respective drawbacks. For instance, the sieving apparatus is employable at most for measuring particles of the extent of 5 .mu.m and cannot be used in the recent technique which is required to have a measuring range extending to less than 0.1 .mu.m. The method in which the solid content in liquid is detected suffers the inconvenience that the size of employable measuring cell cannot be diminished. In the apparatus where the sedimentation of particles is detected by the intensity of transmitted light, a part of incident light is absorbed by the liquid medium during passing through a suspension. An error in measuring due to an amount of such an absorption is usually corrected by multiplication of the measure by a correction factor called absorption coefficient, the absorption coefficient depending on the nature of used measuring apparatus. However, the validity of this correction is open to question. As for the apparatus where the intensity of scattered light or the diffraction pattern is employed, errors are brought about frequently in the measurement.